Inspection operations are imposed throughout manufacturing processes to insure that the product being produced conforms to the manufacturer's quality standards. Semiconductor manufacturing is no exception. Inspection for defects, for alignment tolerances, and for critical dimension control are just a few of the characteristics of a semiconductor device which are inspected during wafer fabrication processes. Once wafer fabrication is complete, the wafer moves to assembly operations for packaging. Within assembly, inspections occur to insure, for example, that a semiconductor die is aligned properly within a package, that the appropriate number of wire bonds or solder bumps are formed on a device, and that the package leads are coplanar.
During each of these inspection processes, an operator is charged with comparing the device being inspected to a standard which has been approved as an acceptable level of quality. The accepted standard can take many forms, but is very often simply a piece of paper noting in words or with a drawing what an acceptable product should look like. While such "paper standards" have the advantage of simplicity, use of paper standards also impose a high degree of human error.
One example of a paper standard which is sometimes used by semiconductor manufacturers is the use of a paper wire bond diagram to inspect the configuration of wire bonds of a semiconductor device. Some semiconductor devices are designed such that not all bond pads of a die are wire bonded to a corresponding lead, or more commonly that not all lead of a designed package are wire bonded to a die bond pad. In order for an operator to understand which bond pads and which lead are to include wire bonds, a diagram is created on paper to indicate where wire bonds should be located. To inspect an actual wire bonded device, an inspector views the device through a microscope and compares the image as magnified by the microscope optics to the paper wire bond diagram. Having to repeatedly view the image of the device under the microscope and turn away to view the paper wire bond diagram creates a number of opportunities for error. For instance, operators can lose their place in making a comparison, creating the potential for portions of the device to pass without inspection. Furthermore, the repeated motion of viewing a microscope image and then viewing a paper image increases cycle time and reduces throughput during the inspection process. Also, because the paper wire bond diagram only marginally presents the actual image as seen under the microscope, use of a paper diagram tends to make the inspection process tedious, time consuming, confusing, and susceptible to error.
With the emergence of highly advanced manufacturing and inspection equipment, some inspection operations have the potential for being fully automated. By incorporating optical recognition capability and integrated software, some semiconductor manufacturing and inspection equipment is available which does an electronic comparison between the device being inspected and a stored electronic file containing information about a manufacturer's acceptable standards. For example, a digitized version of the device being inspected is generated and is compared to a digitized version of an accepted standard. The comparison of the two digitized files is performed by a computer, and the results of the comparison provide an "accepted" or "rejected" output. In an ideal world, such a sophisticated digital comparison would seem to be the perfect solution. However, in a manufacturing world, such a solution is sometimes not possible. The sophisticated equipment necessary to perform such automated inspections is very expensive. Moreover, the time it takes for the equipment to do the comparison and to provide a result only inhibits a manufacturer's goal of reducing total cycle time. Furthermore, the systems are not usually entirely automatic. Some human intervention is still needed, for example to make close judgement calls.
Therefore, a need exists for an improved inspection process for semiconductor devices wherein an inspection can be accomplished in a very quick, efficient manner, with much smaller room for error as compared to prior art paper standard techniques. Moreover, it is desirable for such an inspection method to be practiced with minimal capital investment.